If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You will be required to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Monkey Wrench Tankless

Just to throw a monkey wrench into current tankless discussions, I checked my water temperature this morning. 48 degrees F.

The R98 Rinnai with a 237,000 BTU input would give roughly 5.5 gpm this morning.

That's not too bad in my opinion. But remember, that's the larger single unit.

Two showers running and it's over for any other fixture. Turn on a washing machine in the morning and only one shower. No faucets or anything else or you'll get volume reduction.

Just want to point out what some forget is you must size these things for the business or families lifestyle during the COLDEST GROUND WATER TEMPERATURE.

Else you're going to get callbacks. Many times that puts you in a position of installing TWO or a piggyback tank configuration that makes the whole thing redundant and/or unsellable due to installation & maintenance costs.

Great point there JCsPlumbing, many people overlook the winter temperatures of the incoming water, and wonder why they can not use as much water as they where able to in the summer.

Most manufactures tell you not to size for the amount of people in the home or their lifestyle. Size it for the home period. In other words if they have a 3 bathroom home, with a washing machine, and a dishwasher you need to do the math and size the tankless system in the case that all showers , laundry, and dishes are being done.

But that is the trouble there is many out there that do not want to spend the money involved to install a properly sized system. And there are people out there willing to install an undersized system for the quick buck.

Now I would of recommended going with a pair of R75LSi units with a 75º Temperature rise you would get 4 gpm. So with two units it would yield 8 gpm which would of been able to handle you two showers plus laundry. Also the other benefit of having two units is redundancy. If one unit goes down for any reason, you have the other one that will still provide you hot water till you get the other unit back up.

Yes the way I want to do it would cost a little more than installing a single R98 unit, but I feel it worth the extra few dollars to be able to use everything as needed and have the piece of mind.

Last edited by SewerRatz; 01-13-2010, 10:58 AM.
Reason: added part of my post I missed doing a cut and paste.

Just to throw a monkey wrench into current tankless discussions, I checked my water temperature this morning. 48 degrees F.

The R98 Rinnai with a 237,000 BTU input would give roughly 5.5 gpm this morning.

That's not too bad in my opinion. But remember, that's the larger single unit.

Two showers running and it's over for any other fixture. Turn on a washing machine in the morning and only one shower. No faucets or anything else or you'll get volume reduction.

Just want to point out what some forget is you must size these things for the business or families lifestyle during the COLDEST GROUND WATER TEMPERATURE.

Else you're going to get callbacks. Many times that puts you in a position of installing TWO or a piggyback tank configuration that makes the whole thing redundant and/or unsellable due to installation & maintenance costs.

At least for my area and the average income/lifestyle.

J.C.

THAT IS THE BIGGEST PROBLEM I HAVE SEEN WITH A TANKLESS THE PLUMBER OR HOMEOWNER WANTS THE CHEAPEST ONE FOR THE DOLLAR
AND NOT NECSSARY THE BEST ONE FOR THE USE !

I was installing a pair of customer provided Noritz tankless units today for a commericial install and I gotta say they are very nice!

Stainless steel front panel is a great improvement over the white

I also noticed that they have 250K BTU input capacity while the largest Rinnai I install (9.4LSI) has a 199K Input capacity (if I remember right).

Noritz largest model is the NC380 @ 380K Btu which will give you a flow rate of 8.9gpm @ a 70º temp rise. The largest Rinnai is the R98LSi which is 237K Btu which can give a flow rate of 5.5gpm @ a 70º temp rise.

Your number is correct for the R94LSi it is 199K Btu which will flow 4.8gpm @ a 70║ temp rise.

The Noritz stainless steel casings if their commercail models while the off white models are the residential units.

Noritz largest model is the NC380 @ 380K Btu which will give you a flow rate of 8.9gpm @ a 70º temp rise. The largest Rinnai is the R98LSi which is 237K Btu which can give a flow rate of 5.5gpm @ a 70º temp rise.

Your number is correct for the R94LSi it is 199K Btu which will flow 4.8gpm @ a 70║ temp rise.

The Noritz stainless steel casings if their commercail models while the off white models are the residential units.

When you figure the flow rate, that is obviously all hot water, right? So when you size a shower that has ,lets say 10gpm flow rate, would you figure 70% of that is hot water, therefore the heater is going to need a 7gpm flow rate, just for the shower?

Comment

The unit that really impresses me is the Takagi T-M50 its two 190,000 BTU units in one case. So outside the case plumbing and venting is as if it was one unit. connecting the two heat exchangers is all done on the inside for us. Also it allows for the redundancy I always talk about when installing two units. This way if one side of this unit goes down for any reason the other side will work independently till repairs are made.

Thing is if you install this or any unit that is over 199K Buts (this unit is actually considered 380K) in any commercail environment, you must get the one with the ASME ratting.

When you figure the flow rate, that is obviously all hot water, right? So when you size a shower that has ,lets say 10gpm flow rate, would you figure 70% of that is hot water, therefore the heater is going to need a 7gpm flow rate, just for the shower?

There is two schools of thought on this.

Some contractors like to set the output temperature to 115º , so people would run full hot in the shower(most studies show people prefer to shower in 115 to 110º water temps). So you would size it for full flow for the temperature degree rise to reach the 115º.

I do not like that school of thought. I prefer to supply 120º (normal setting on most tank heaters) and figure most people will shower at the setting of 110º So the flow rate of hot water in a 10 GPM shower mixed with cold water would be more like 90% so the GPM would be 9 GPM.

Comment

Once inspected, myself and the homeowner decided to experiment on his 4 bath home.

We turned on the KS, two lavs, two showers and only got a slight reduction in pressure at that point.

All of a sudden he comes up to me, very disappointed and says he thinks the unit is no good.

He'd turned on the Roman tub filler in his master bath, with all the other fixtures running, a total of 6 GPM on those puppies, it took me a minute to get across the point that even if he had guests, it wasn't very likely that all those fixtures would be running at the same time coincidentally while he filled the Jacuzzi.

I'd wager the water temperature was at least 50 to 55 degree's at that time, likely lower, I'm north of you.

Where I think you might be mistaken is the assumption that each fixture's GPM rating is all hot.

A 2.5 GPM shower, for example, is combined hot and cold, granted predominantly hot, but not the full 2.5.

I know Rinnai and Rheem units to be roughly par on performance, and if the Rheem held up with that many fixtures, I'm sure the Rinnai would too.

Once inspected, myself and the homeowner decided to experiment on his 4 bath home.

We turned on the KS, two lavs, two showers and only got a slight reduction in pressure at that point.

All of a sudden he comes up to me, very disappointed and says he thinks the unit is no good.

He'd turned on the Roman tub filler in his master bath, with all the other fixtures running, a total of 6 GPM on those puppies, it took me a minute to get across the point that even if he had guests, it wasn't very likely that all those fixtures would be running at the same time coincidentally while he filled the Jacuzzi.

I'd wager the water temperature was at least 50 to 55 degree's at that time, likely lower, I'm north of you.

Where I think you might be mistaken is the assumption that each fixture's GPM rating is all hot[/B].

A 2.5 GPM shower, for example, is combined hot and cold, granted predominantly hot, but not the full 2.5.

I know Rinnai and Rheem units to be roughly par on performance, and if the Rheem held up with that many fixtures, I'm sure the Rinnai would too.

You would be correct in that my math of the fixture use is wrong. I didn't consider potentially lower temperatures at the showers.

I did want to remind everyone to allow for water temperatures at the coldest time of the year so they would not get a potential callback/problem.

it's one thing if you install this on new construction where you have a good excuse that the head is rated for 2.5gpm, but in reality the homeowner who just spent thousands of dollars can care less about the 2.5gpm rule.

my deck mounted 3/4'' tub valve is not even close to par with the cold flow.

my tank heater had no problem keeping up with the tub.

but then again i now have an extra $5.00 a month to try and make joey happy

rick.

phoebe it is

Comment

I've spent a good part of this week so far explaining to customers why their hot water is either cold or not keeping up. Our incoming water is usually no lower than 65 deg. Many places the temp is down to the mid 30's. Another thing, tank heaters with exposed recirc. lines( I know, should be insulated but not my install) were loosing heat faster than the tank could make it.